It probably means different things for different people, because like every other fandom, it's kinda arbitrary.

I was kind of purist. I started with TOS, but TNG, DS9, and VOY were right then too. Didn't care as much for Voyager, but it was ok. Skipped Enterprise completely. I have TAS but haven't watched it. Actively disliked the Kelvin movies. I've missed all the new stuff because I don't stream, except Lower Decks, which I find delightful. I'm gonna pick up Picard and SNW soon.